Rizzo mysteriously removed from Iowa's game

The debate has been going on for weeks, but "Rizzo Watch 2012" may have officially begun Sunday night with a series of tweets from the Triple-A Iowa Cubs twitter account regarding first base prospect Anthony Rizzo:

Samson pinch-hits for Rizzo in top 6 and stays in game at 1B. Iowa leads Memphis 3-1 in middle of 6th. Iowa Cubs (@IowaCubs) May 28, 2012We have no further information on Rizzo. FWIW: All transactions involving Iowa Cubs players are always announced first in Chicago. Iowa Cubs (@IowaCubs) May 28, 2012Radio report: Rizzo leaves Iowa Cubs dugout, heads to clubhouse. Iowa Cubs (@IowaCubs) May 28, 2012
At this time, this could mean absolutely nothing other than a manager choosing to remove his best hitter in the middle of a game. If that's not the case, the other options would range from the unfortunate (injury) or a call-up to the major leagues.

David Kaplan has weighed in with the following tweet:
Excellent source in Des Moines tells me that Rizzo is not getting called up to the Cubs. Repeat: NOT GETTING CALLED UP. David Kaplan (@thekapman) May 28, 2012